Caribbean-Florida Water Science Center
Evapotranspiration Network in Florida
Project Chief: Barclay Shoemaker, Mike Wacker
Micrometeorological station at Starkey pasture, Pasco County, Florida.
Evapotranspiration (ET) is a large part of the hydrologic budget in Florida, ranging from 30 to over 100% of average precipitation. In the past, the accuracy of hydrologic models, basin-scale studies, water budgets, and other hydrologic analyses throughout the State was reduced because of the lack of accurate estimates for this large water loss. Scientists and water managers in Florida would benefit from having a network of consistently operated high-quality ET stations from representative land use areas using state-of-the-science methods. Another recurring problem in hydrologic simulation and water allocation strategies in Florida has been inconsistencies between the five State of Florida Water Management Districts in methods for computing the potential and reference ET. Potential ET (PET) is a necessary data input for most hydrologic simulation models. Reference ET (RET) is a necessary input for WMD water allocation to water users.
1) Measure actual ET from representative land covers in Florida
2) Develop predictive models to estimate ET from environmental variables such as depth to water, season, and net radiation
3) Provide 2-km gridded satellite-based estimates of potential and reference ET on a daily time scale for the entire State
Components of the surface-energy balance used to estimate evapotranspiration.
For ET stations, evapotranspiration and other variables are measured for between 2 and 10 years to develop relations between measured ET and environmental factors such as weather, groundwater levels, and plant cover conditions. Data collected included:
The following site types were measured: lake, estuary, shallow and deep water-table pasture, hay field, pine forest, wetland forest, cypress, wet prairie, marsh, citrus, sawgrass, palmetto/scrub, and urban land use.
For the satellite-based gridded PET and RET, a method was developed that converts Geostationary Satellite System (GOES)-satellite solar radiation data to these commonly used ET estimates; the approach was validated using PET and RET from the ground-based sites.
Annual ET rates at land-based sites vary from a low of 570 mm (22.4 inches) at a pasture with a deep water table to 1340 mm (53 inches) at a sawgrass marsh. Rates at open-water sites exceed 1500 mm (59 inches). Daily values of ET are archived in the USGS NWIS database and can be accessed at https://fl.water.usgs.gov/et/etdata.html
Shoemaker, W. B., Lopez, C. D., Duever, M. J., 2011, Evapotranspiration over spatially extensive plant communities in the Big Cypress National Preserve, southern Florida, 2007-2010: https://pubs.usgs.gov/sir/2011/5212/